How do you pan on a mac?
Shift + two finger scroll around. You don't need a three-button mouse, as Blender has excellent multi-touch trackpad* support. (You can two-finger scroll to orbit around, and pinch to zoom, too! It even supports horizontal scrolling of header regions/tab bars.)

*Or a Magic Mouse, which is basically a mouse with a trackpad on top. Never actually tried one with Blender, though.